Superconductors

ABSTRACT

A superconductor assembly comprising at least one superconductor composite of at least one element of a superconductor material which is superconductive below a critical temperature embedded in a matrix of at least one material which is not superconductive at said critical temperature, assembled to at least one component consisting of one or more materials which are not superconductive at said critical temperature to provide a tubular assembly having at least one passage for fluid coolant.

United States Patent Woolcock et a1.

[54] SUPERCONDUCTORS [72] Inventors: Alan Woolcock; Anthony Clifford Barber,

both of Lichfield, England Imperial Metal Industries Kynock Limited, Witten, Birmingham, England [22] Filed: June 11,1970

[21] Appl.No.: 45,501

[73] Assignee:

[30] Foreign Application Priority Data June 19, 1969 Great Britain ..31,083/69 52 US. Cl ..174/15 c, 174/27, 174/126 CP, 174/128, 174/1310. 6, 335/216 511 Int. Cl. ..H0lb 7/34 58 Field oiSearch ..174/15 0, 15 SC, 126,27, 33, 174/128, DIG. 6, 126 R, 126 LP; 335/216 [56] References Cited UNITED STATES PATENTS 3,544,706 12/1970 Aupoix ..l74/l5 C 3,502,789 3/1970 Barber ..,.174/l5 C 2,440,668 4/1948 Tarbox ...l74/15 X 3,427,391 2/1969 Bernert et a1. 174/15 0 1151 3,657,466 [451 Apr. 18, 1972 3,472,944 10/1969 Morton et a1. ..l74/ 15 C FOREIGN PATENTS OR APPLICATIONS 887,012 5/1953 7 Germany ..l74/15 C 284,774 2/1928 Great Britain ..174/ 15 C OTHER PUBLICATIONS H. E. Cline, B. P. Strauss, R. M. Rose, & J. Wulff, Superconductivity of a Composite of Fine Niobium Wires in Copper, in Journal of Applied Physics. Vol. 37 No. l p. 58 1966 Primary Examiner-Laramie E. Askin Assistant ExaminerA. T. Grimley Attorney-Cushman, Darby & Cushman [5 7] ABSTRACT A superconductor assembly comprising at least one superconductor composite of at least one element of a superconductor material which is superconductive below a critical temperature embedded in a matrix of at least one material which is not superconductive at said critical temperature, assembled to at least one component consisting of one or more materials which are not superconductive at said critical temperature to provide a tubular assembly having at least one passage for fluid coolant.

10 Claims, 8 Drawing Figures Patented -April 18, 1972 3,657,466

2 Sheets-Sheet 2 SUPERCONDUCTORS FIELD OF THE INVENTION This invention relates to superconductors and to methods of manufacture thereof. The invention is specifically concerned with a superconductor assembly wherein there is provided a There has been suggested a superconductor assembly in which at least one element of a superconductor material which is superconductive below a critical temperature, is embedded in a matrix forming the wall of the assembly, the matrix preferably being of a thermally and electrically conductive material, such that the flow of liquid helium through the hollow interior of the assembly will serve to maintain the temperature of the superconductor material below its critical temperature.

It is an object of the invention to provide a superconductor assembly which is provided with a passage for fluid coolant, and which can be manufactured readily in substantially longer lengths than those which have been successfully achieved in connection with the prior suggestion.

SUMMARY OF THE INVENTION In accordance with the invention, a superconductor assembly comprises at least one superconductor composite comprising at least one element of a superconductor material which is superconductive below a critical temperature, embedded in a matrix of at least one material which is not superconductive at said critical temperature, said composite being assembled to at least one component consisting of one or more materials which are not superconductive at said critical temperature to provide a tubular assembly having at least one passage for fluid coolant to maintain said superconductor material at a temperature below its critical temperature.

Preferably said composite is enclosed within said at least one component to provide at least two passages for fluid coolant.

Preferably said composite is assembled to said at least one component by being positively securedthereto, for example by welding or soldering, but if said composite is totally enclosed by said at least one component, the assembly together thereof may either be by being positively secured thereto or said composite may merely be lodged in position.

If there is a single component in the superconductor assembly, preferably it is either secured to itself or to at least one composite to define said passage for fluid coolant, or altematively the component is of integral tubular shape.

Preferably said superconductor material is a superconductor alloy of niobium and titanium, for example niobium 44 weight percent titanium.

Preferably further said at least one material of the matrix of the composite is high-conductivity copper only, but alternatively the matrix material may be a copper-base alloy having a higher electrical resistivity than that of commercially pure copper, for example a cupro-nickel alloy. In this case the cupro-nickel alloy either extends through the whole, and constitutes, the matrix material, or it is located as an uninterrupted layer around said element of a superconductor material, the remainder of the matrix being composed of some other material which is not superconductive below said critical temperature.

Preferably there are provided a plurality of elements of superconductor material in said superconductor composite.

DESCRIPTION OF THE DRAWINGS The invention will now be more particularly described with reference to the accompanying diagrammatic drawings in which:

FIG. 1 is a cross-sectional view of a first example of the invention;

FIG. 2is a cross-sectional view of a modification of the first example;

FIG. 3 is a cross-sectional view of a further modification of the first example;

FIG. 4 is a cross-sectional view of a second example of the invention;

FIG. 5 is a cross-sectional view of a third example of the invention;

FIG. 6 is a cross-sectional view of a fourth example of the invention;

FIG. 7 is a cross-sectional view of a further modification of the first example; and

FIG. 8 is a perspective view of a fifth example of the inventIOII.

DESCRIPTION OF THE PREFERRED EXAMPLES In the first example of the invention, FIG. 1 shows a tubular superconductor assembly 10 made from a superconductor composite strip 11 which is assembled to two U-shaped nonsuperconductor components 12.

In more detail, the superconductor composite strip 11 comprises a large number of filaments 13 of the superconductor alloy niobium 44 weight percent titanium which has a critical temperature in zero magnetic field of about 92 K, which are embedded within a matrix of high-conductivity copper 14. Copper has no superconductive properties at 92 K or 4.2 K. The strip 11 is manufactured by any convenient process, for example by the provision of a plurality of superconductor rods in corresponding apertures in a copper billet to produce an assembly, the assembly being extruded and drawn and finally flattened to produce the configuration illustrated in FIG. 1. A further example of a convenient process for manufacturing the strip 11 is by rolling face to face a number of copper or other ductile non-superconductor strips with one or more superconductor wires interposed between each two adjacent strips.

Each non-superconductor component 12 is of high-conductivity copper only, and comprises two parallel sides 15 which are secured together by a base 16, the interior of the center of the base 16 being recessed to provide a groove 17 of a suitable dimension for receiving the corresponding edge of the superconductor composite strip 11. Each component 12 may be manufactured as a flat strip into which is rolled the groove 17, followed by the bending upwardly of each of the sides 15. In this way large lengths of each component 12 can be manufacturedv by the securing together of ends of adjacent copper strips, followed by the bending operation, and the bending operation has a particular virtue in that this will provide a certain amount of work-hardening of the copper in the vicinities of the resulting comers.

The assembly of FIG. 1 is produced by the location of the two components 12 face to face and sandwiching the com posite superconductor strip 11 with its edges in the corresponding grooves 17, whereupon the facing ends of the sides 15 are welded together in any suitable fashion. To obtain an adequate weld with the minimum generation of heat, it is preferred that electron beam welding be used.

As already mentioned, the components 12 can be manufactured in almost indefinite lengths, and this also applies to the composite superconductor strip 11, because this always exists as a strip and it is therefore relatively easy for the ends of successive strips to be secured together with minimum electrical resistance, for example by overlapping adjacent ends, explosively welding them together, and removing excess material to leave the joint with the same cross-section as that of the remainder of the strips.

In use, the tubular superconductor assembly of FIG. 1 is usually wound as the turns of an electro-magnet, and it is then used at a temperature below the critical temperature of the superconductor material. This is achieved initially, and is maintained, by the pumping of liquid helium at about 4.2 K or pressurized supercritical helium at just over 4.2 K through the two passages 18,19 formed one to each side of the strip 11, and within the two components 12. Confinement of the helium in this way ensures maximum contact thereof with the faces of the strip 11, and enables pressurization to be used. Also the rapid and uniform circulation which can be achieved will serve to remove rapidly any bubbles of gaseous helium formed in liquid helium, or any helium which has absorbed heat, as quickly as possible from the vicinity concerned. In addition, the components 12 provide extra strength for the strip 11, and this is supplemented by the work-hardening of the corners which has been mentioned above. Still further, as well as the high-conductivity copper of the strip 11 having the function of heat removal and acting as a heat sink for any heat generated in the superconductor filaments 13, this will be aided by the high-conductivity copper of the components 12. Also the fact that there are two cooling passages 18,19 decreases the possibility of a length of the assembly becoming heated to above the critical temperature of the superconductor material because the metal surface available for cooling by helium is increased, and the rate of enlargement of any small heated length is minimised because of the containment in one of the passages 18,19 of heated coolant.

In the first example, as just described, the edges of the strip 11 are merely lodged in the corresponding grooves 17 provided in the components 12. However, if required, the tubular assembly may be strengthened, and the thermal and electrical contact between the strip 11 and the components 12 may be enhanced, by the welding of the edges of the strip 11 into the groove 17. This is preferably accomplished by use of the electron beam welder along the mid line of the base 16 to each of the components 12.

In a modification of the first example, there may be pro vided more than one strip 11 in the interior of the tubular assembly, for example there being two such strips which are parallel to, and spaced apart from, each other. In this example, there will then be three passages through the interior of the assembly 10. This is illustrated in FIG. 2 of the drawings with the passages 20,21,22.

In yet another modification, the two components 12 may be integral with each other across one of the welds illustrated in FIG. 1, there then being a single component which is bent into a box shape, in so doing receiving the strip 11, and there is then only a single weld required to close the assembly.

FIG. 3 shows a further modification of the example of FIG. 1 in which the strip 11 is extended through the entire thickness of the components 12 of FIG. 1, in which case welding is effected between the free end of each arm of two U-shaped components 30, with the facing surface of the central strip 11.

' FIG. 4 shows a second example of the invention in which a single strip of high-conductivity copper is bent into a rectangular box shape 31, and is welded into this position as shown at 32. Located within the strip 31 prior to welding is a superconductor composite strip 33 which is lodged diagonally across the interior of the rectangular box shape. If required, the strip 33 may be secured in position by electron beam welding after the rectangular box shape has been achieved. The strip 32 separates two coolant passages 34,35.

FIG. 5 of the drawings illustrates a third example of the invention in which a tubular superconductor assembly is produced by the welding together of a single U-shaped cornponent 44 of a material which is not superconductive at the critical temperature of the superconductor material, for example high-conductivity copper or aluminum, with one side of a composite superconductor strip 45 which is of the same general construction as the strip 11 of FIG. 1. Thus in this instance one entire side of the tubular assembly is constituted by the composite superconductor strip 45, and the other three sides are constituted by the U-shaped component 44. The tubular assembly of FIG. 5 contains a single coolant passage 46.

In modifications of the third example, more than one side of the tubular assembly may be constituted by a composite superconductor strip, for example the side opposite to that of the strip 45 illustrated in FIG. 5, can be constituted by a further such strip. Thus in this modification (not shown), two composite superconductor strips 45 are located parallel to but spaced from each other, and they are bridged by two copper strips which thereby define a rectangular tube containing the coolant passage 46.

FIG. 6 illustrates a fourth example of the invention, in which there is provided a composite superconductor strip 47 which is secured onto one side of a rectangular copper tube 48. Securing is typically effected by soldering, as illustrated at 49. Hence, in this example the component of non-superconductor material already exists in tubular form, with a single coolant passage 50, prior to being provided with its composite superconductor strip. If required, more than one side of the copper tube 48 can be provided with a composite superconductor strip.

In modifications of all of the examples, other superconductor materials can be used, and the superconductor filaments can exist in any number, or there can be only one filament. In this latter case, the superconductor filament will usually take the form of a strip located within the matrix of the non-superconductor material. This is illustrated in FIG. 7 with the superconductor 51 in the matrix 14.

The sizes of the superconductor filaments can be varied as required, and in particular they can be decreased to less than 0.005 cm in order to provide inherent stability against flux jumps, and they can be twisted and transposed one over another in order to minimize flux linkage between the filaments. For an inherently stable superconductor the matrix material is still preferably high conductivity copper, but alternatively there can be used a matrix material which has a lower electrical conductivity than that of high-conductivity copper, so that suitable copper alloys such as cupro-nickel can then be used alone as the matrix material or as a layer around each superconductor filament in a matrix of copper, or as a layer between two rings of filaments. Alternatively, if high-conductivity is still required, high-conductivity copper can be replaced by aluminum or other highly conductive metals such as indium or silver.

In a further modification, the tensile strength of the tubular superconductor assembly can be increased by the incorporation within each non-superconductor component of a number of strengthening filaments, for example of stainless steel or a strong titanium alloy. As an alternative, one or more of the external surfaces of the tubular superconductor assembly can be secured to a tape of a stronger material, for example stainless steel.

FIG. 8 of the drawings illustrates the fifth example of the invention which comprises a tube 60 of non-superconductor material, for example high-conductivity copper, workhardened copper, aluminum or stainless steel, around which are wound and soldered typically 24 wires 61. Each wire 61, which can be of rectangular or circular cross-section, will normally be a composite of a plurality of superconductor filaments 62 embedded in a matrix 63 of non-superconductor material, for example high-conductivity copper or cupronickel, but some of the wires 61 can be of high-conductivity copper only, to provide electrical shunting capacity and thermal absorption and conductivity, and further wires 61 can be of strengthening material, for example stainless steel. The filaments 62 in each composite wire 61 can be of less than 0.005 cm diameter and twisted to such a degree as to provide intrinsic stability in each wire 61, the transposition of each wire 61 around the tube 60 giving good overall stability. More then one layer of wires 61 can be provided. The tube 60 can be of square (as shown) or other cross-sectional shape.

We claim:

1. A superconductor assembly comprising at least one superconductor composite in the form of an elongated strip comprising a plurality of elements of a superconductor material which is superconductive below a critical temperature, extending longitudinally within said strip and embedded in and in electrical and thermal contact with a matrix of at least one material which is electrically and thermally conductive and is not superconductive at said critical temperature, said composite being assembled to two channel-shaped components consisting of one or more materials which are not superconductive at said critical temperature and which have high electrical and thermal conductivity, said components being joined edge-to-edge in surrounding relationship to said composite to provide a tubular assembly having at least two passages for fluid coolant to maintain said superconductor material at a temperature below its critical temperature.

2. A superconductor assembly as in claim 1 wherein there are a plurality of spaced-apart parallel composites surrounded by said channel-shaped components.

3. A superconductor assembly comprising at least one superconductor composite in the form-of an elongated strip comprising a plurality of elements of a superconductor material which is superconductive below a critical temperature, extending longitudinally within said strip and embedded in and in electrical and thermal contact with a matrix of at least one material which is electrically and thermally conductive and is not superconductive at said critical temperature, said composite being assembled to at least one component consisting of one or more materials which are not superconductive at said critical temperature and which have high electrical and thermal conductivity to provide a tubular assembly having at least one passage for fluid coolant to maintain said superconductor material at a temperature below its critical temperature, said component being bent to form a rectangular tube and said composite being disposed diagonally across and in contact with the bore of the tube.

4. A superconductor assembly of the type including at least one superconductor composite comprising at least one element of a superconductor material, which is superconductive below a critical temperature, embedded in and in electrical and thermal contact with a matrix of at least one material which is electrically and thermally conductive and is not superconductive at said critical temperature, the said composite being assembled with at least one tubular component consisting of at least one material which is not superconductive at said critical temperature and which has a high electrical and thermal conductivity to provide a tubular assembly having at least one passage for fluid coolant to maintain said superconductor material at a temperature below its critical temperature, wherein the improvement comprises the at least one composite being in the form of a wire helically wound around and in contact with the tubular component.

5. The superconductor assembly of claim 4 wherein each of said at least one composites incorporates a plurality of elements of a superconductor material.

6. The superconductor assembly of claim 4 wherein there are a plurality of composites helically wound around the tube.

7. The superconductor assembly of claim 4 wherein each wire is twisted.

8. The superconductor assembly of claim 4 wherein the tube is of circular or rectangular cross-section.

9. The superconductor assembly of claim 4 wherein the superconductor material is a superconductor alloy of niobium and titanium.

10. The superconductor assembly of claim 9 wherein the alloy is niobium 44wt. percent titanium. 

1. A superconductor assembly comprising at least one superconductor composite in the form of an elongated strip comprising a plurality of elements of a superconductor material which is superconductive below a critical temperature, extending longitudinally within said strip and embedded in and in electrical and thermal contact with a matrix of at least one material which is electrically and thermally conductive and is not superconductive at said critical temperature, said composite being assembled to two channel-shaped components consisting of one or more materials which are not superconductive at said critical temperature and which have high electrical and thermal conductivity, said components being joined edge-to-edge in surrounding relationship to said composite to provide a tubular assembly having at least two passages for fluid coolant to maintain said superconductor material at a temperature below its critical temperature.
 2. A superconductor assembly as in claim 1 wherein there are a plurality of spaced-apart parallel composites surrounded by said channel-shaped components.
 3. A superconductor assembly comprising at least one superconductor composite in the form of an elongated strip comprising a plurality of elements of a superconductor material which is superconductive below a critical temperature, extending longitudinally within said strip and embedded in and in electrical and thermal contact with a matrix of at least one material which is electrically and thermally conductive and is not superconductive at said critical temperature, said composite being assembled to at least one component consisting of one or more materials which are not superconductive at said critical temperature and which have high electrical and thermal conductivity to provide a tubular assembly having at least one passage for fluid coolant to maintain said superconductor material at a temperature below its critical temperature, said component being bent to form a rectangular tube and said composite being disposed diagonally across and in contact with the bore of the tube.
 4. A superconductor assembly of the type including at least one superconductor composite comprising at least one element of a superconductor material, which is superconductive below a critical temperature, embedded in and in electrical and thermal contact with a matrix of at least one material which is electrically and thermally conductive and is not superconductive at said critical temperature, the said composite being assembled with at least one tubular component consisting of at least one material which is not superconductive at said critical temperature and which has a high electrical and thermal conductivity to provide a tubular assembly having at least one passage for fluid coolant to maintain said superconductor material at a temperature below its critical temperature, wherein the improvement comprises the at least one composite being in the form of a wire helically wound arOund and in contact with the tubular component.
 5. The superconductor assembly of claim 4 wherein each of said at least one composites incorporates a plurality of elements of a superconductor material.
 6. The superconductor assembly of claim 4 wherein there are a plurality of composites helically wound around the tube.
 7. The superconductor assembly of claim 4 wherein each wire is twisted.
 8. The superconductor assembly of claim 4 wherein the tube is of circular or rectangular cross-section.
 9. The superconductor assembly of claim 4 wherein the superconductor material is a superconductor alloy of niobium and titanium.
 10. The superconductor assembly of claim 9 wherein the alloy is niobium 44wt. percent titanium. 